1. Field of the Invention
The present invention relates to a brake controller and, more specifically, to a controller for controlling the braking force of a brake provided on a power transmission path.
2. Description of the Background Art
Conventionally, techniques for controlling the braking force of a brake based on an amount of operation of a brake pedal by a driver have been proposed. By way of example, Japanese Patent Laying-Open No. 2000-313320 discloses a braking force control unit capable of reducing a sense of abruptness at the time of starting for realizing a smooth start of a vehicle. The braking force control unit operates such that the driving force is transmitted from a motor to driving wheels even when the stepping-on of an accelerator pedal is released at a vehicle speed not higher than a prescribed speed as long as a driving range is selected in a transmission, and the magnitude of the driving force to be transmitted to the driving wheels is switched between large and small in accordance with the state of stepping-on of a brake pedal. When the brake pedal is stepped on, the braking force control unit reduces the driving force to be smaller than when the stepping-on of the brake pedal is released. The braking force control unit includes a braking force retaining means capable of retaining the braking force on the vehicle after releasing the stepping-on of the brake pedal. The braking force retaining means reduces gradually the braking force when the driving force is increased to a large value after stepping-on of the brake pedal is released.
According to the braking force control unit disclosed in the laid-open application described above, the braking force is reduced gradually, and therefore, the sense of abruptness at the time of starting of a vehicle, which was experienced as the braking force was reduced at once, can be suppressed.
In the braking force control unit disclosed in the laid-open application described above, however, though the braking force is reduced at once when the acceleration pedal is stepped on after releasing the brake pedal, the braking force is reduced gradually when the acceleration pedal is not stepped on. Assume, for example, that a vehicle is crawling along in a traffic jam, following the car in front, utilizing creep torque of an automatic transmission. When the braking force is reduced gradually after the brake is released, forward driving force is generated after the creep torque exceeds the braking force. Thus, it takes time until the driving force is generated after the release of the brake pedal, resulting in an unsatisfactory response.
On the other hand, if the braking force is reduced at once after releasing the brake pedal, the vehicle body may have a shock.